Intake poppet valves and exhaust poppet valves of an engine cylinder may be selectively deactivated to conserve fuel. The intake and exhaust valves may be selectively activated and deactivated via electromechanical actuators that may from time to time leave the valves in a deactivated state. On the other hand, the electromechanical actuators may allow the intake and exhaust valves to continue to operate even though the intake and exhaust valves were commanded to a deactivated state. If the intake and exhaust valves continue to operate when the valve actuators are commanded to deactivate the valves, fresh air may be pumped to the engine's exhaust system where it may affect catalyst activity, thereby degrading vehicle emissions. Conversely, if the valves continue to be deactivated after the valve actuators are commanded to activate the valves, the engine may produce less power than is desired and fuel may accumulate in cylinders having valves that remain deactivated.
One way to determine whether or not valve actuators are activating and deactivating intake and exhaust poppet valves may be to measure cylinder pressure during a cycle of a cylinder. Alternatively, sensors may be placed to sense the position of the valve actuators to determine if the valve actuators reach their commanded position. However, cylinder pressure sensors and valve actuator position sensors may increase system cost significantly. Therefore, it may be desirable to provide a way of determining if intake and exhaust valve actuators are performing as is expected without having to deploy cylinder pressure sensors or valve actuator position sensors.
The inventor herein has recognized the above mentioned issues and has developed an engine operating method, comprising: rotating an engine without combusting fuel via a controller; indicating valve actuator degradation in response to lack of a temperature increase in an exhaust system after commanding activation of poppet valves of one or more engine cylinders while rotating the engine without combusting fuel; and adjusting operation of the engine in response to the indication of valve actuator degradation.
By sampling a temperature of gases flowing through an exhaust system, it may be possible to provide the technical result of determining whether or not intake and exhaust valve actuators are operating as is expected. In one example, hot exhaust gases may be trapped in one or more engine cylinders after combustion in the engine has ceased. At the same time, intake and exhaust valves of other engine cylinders may operate according to a four stroke engine cycle. The engine may be rotated by an electric machine, absent combustion within the engine, so that air flowing through the cylinders having operating intake and exhaust valves cools gases flowing through the exhaust system. After gas temperatures in the exhaust system have cooled, the trapped hot exhaust gases in cylinders having deactivated valves may then be released to the exhaust system by commanding formerly deactivated intake and exhaust valves to active. If the temperature in the exhaust system increases, it may be judged that the intake and exhaust valve actuators are operating as is expected. However, if the temperature in the exhaust system does not increase, it may be judged that the intake and exhaust valve operators are not operating as is expected because it may be inferred that exhaust gases remain trapped in the engine cylinder or that fresh air failed to enter cylinders and participate in combustion.
The present description may provide several advantages. In particular, the approach may provide improved diagnostics of engine cylinder valve deactivation devices and intake and exhaust valves. Additionally, the approach may provide cylinder diagnostics without increasing system cost. Further, the approach may reduce engine emissions if degraded valve operators are detected.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.